1. Field of the Invention:
This invention relates to a text processing system such as a word processor, and more particularly to a text processing system in which the utilization efficiency of a storage medium can be improved.
2. Description of the Prior Art:
In recent years, text processing systems such as a so-called word processor have come into use in increasing numbers for preparing texts or documents which contain character strings or sentences. Texts prepared on such a text processing apparatus are usually stored on a storage medium such as a magnetic disk or IC memory in a magnetic or electronic form. Since the storage medium such as a magnetic disk has an extremely high recording density as compared with a traditional storage medium such as paper, such storage medium have an advantage in that the space for storing texts can be greatly reduced. A text processing system can permit the easy preparation of a new text by partially modifying a text which has been stored on a storage medium.
In a conventional text processing system, texts are stored on a storage medium such as magnetic disk, by reserving in the storage medium a storage area (called a file) for every one of the texts, and by storing each text in one file. When a plurality of texts containing a sentence(s) common to them are stored on a storage medium, the common sentence(s) must be stored in each of several files, which causes a problem in terms of the efficient utilization of the storage medium. This will be described with reference to FIG. 12.
When two texts A and B having a common sentence "I go to school." are stored on a storage medium, the two texts A and B are stored in two files 120 and 121, respectively. This means that the same sentence exists in both the files 120 and 121, resulting in the wasted use of the storage area of the medium.
In the above-mentioned example, the two files storing respectively the two texts contain only one common sentence. When a new text is prepared by partly modifying a text which have been previously prepared and stored in a storage medium (hereinafter, such a text is referred to as "an old text"), however, it is usual that numerous sentences are commonly stored in both the file for the old text and that for the new text. In many texts actually prepared, stereotyped sentences may account for a relatively large part of the text. When a large number of such documents are prepared using old texts, the use efficiency of a storage area of a storage medium is greatly reduced.